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XRT79L71
PRELIMINARY
415
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
RxOHInd/
RxGapClk
C6
O
Receive Overhead Bit Indicator Output/Receive Gap-Clock Output:
The function of this output pin depends upon whether or not the
XRT79L71 has been configured to operate in the Gapped-Clock Mode.
Non-Gapped Clock Mode - RxOHInd:
This output pin will pulse "high", for one "RxClk" period, coincident to
whenever the Receive Payload Data Output Interface block outputs an
overhead bit via the "RxSer" output pin. This output pin will be held "low"
at all other times. The purpose of this output pin is to alert the System-
Side Terminal Equipment that the current bit (e.g., the one that is cur-
rently residing on the RxSer output pin) is an overhead bit and should
not be processed by the System-Side Terminal Equipment.
The XRT79L71 will update output signal upon the rising edge of RxClk.
Therefore, the user is advised to design (or configure) the System-Side
Terminal Equipment to sample this signal (along with the data on the
RxSer output pin) on the falling edge of the RxClk signal.
NOTE: For E3 Applications, this output pin is active (in the "RxOHInd"
role) if the Receive Payload Data Output Interface block has
been configured to operate in either the Serial or the Nibble-
Parallel Mode. This output pin will be held "low" at all times.
This is in contrast for DS3 applications, in which is pin is only
active for "Serial" Mode operation.
Gapped Clock Mode - RxGapClk:
This particular output pin will function as a "payload bit" output clock sig-
nal. In other words, in this mode, the Receive Payload Output Interface
block will only generate a clock pulse (via this output pin) coincident to
whenever it outputs a payload bit via the RxSer output pin. The Receive
Payload Data Output Interface block will NOT generate a clock edge (via
this output pin) coincident to whenever it outputs an overhead bit via the
"RxSer" output pin. As a consequence, there will be "gaps" within this
particular clock output signal (hence the name "Gapped Clock Mode").
If the XRT79L71is configured to operate in the Gapped Clock Mode,
then the user must design or configure the System-Side Terminal Equip-
ment to sample and latch the "RxSer" data upon the falling edge of the
"RxOHInd/RxGapClk" clock signal.
RxFrame
B6
O
Receive Payload Data Output Interface - Receive Start of Frame
Output Indicator:
The behavior of this output pin depends upon whether the XRT79L71
has been configured to operate in the "Serial" or in the "Nibble-Parallel"
Mode.
Serial Mode Operation
The Receive Payload Data Output Interface block will pulse this output
pin "high" (for one RxCLK period) coincident to whenever it outputs the
very first bit of a new E3 frame via the "RxSer" output pin. This output
pin will remain "low" at all other times.
Nibble-Parallel Mode Operation
The Receive Payload Data Output Interface block will pulse this output
pin "high" (for one RxCLK or "Nibble-Period") coincident to whenever it
outputs the very first nibble of a new E3 frame via the "RxNib[3:0]" output
pins. This output pin will remain "low" at all other times.
TABLE 51: LIST AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE RECEIVE PAYLOAD DATA OUTPUT INTERFACE
BLOCK
SIGNAL NAME
PIN/BALL
NUMBER
TYPE
DESCRIPTION